art wrote:
Roy Lewallen wrote:

Since there's no "typical" Yagi, I presented one which most people would
consider to be worse than average -- one having only a 6 dB front/back
ratio. I also assumed for a starting point that the shape of the rear
lobe (that is, beamwidth and height) is the same as the front lobe. The
first calculation is to determine just what the ratio is of the powers
in the front and rear lobe. The answer is 4:1. That is, the front lobe
contains four times the power of the rear lobe.

I am not interested in front to back for what I am looking for but this
4:1 has my interest
What does it represent

I can't think how I can state it any more clearly than I did in the last
sentence of the text just above which you quoted.

and how did you get it?

When dealing with a power ratio, dB = 10 * log(ratio). Solving for ratio:

ratio = 10^(dB/10)

Here's where you'll probably need to get out that pocket calculator. dB
is 6 (see above text), so ratio = 10^(0.6) ~ 4.

Conversion between ratios and dB is a skill that anyone interested in
antennas should develop. I had assumed that it was part of the knowledge
required to pass a general class amateur exam, but apparently I was
mistaken. If the calculator operations are too complex for you, get a
chart of conversion factors which have already been calculated.

The rear usually has
more than one lobe

True. See the remainder of my previous posting for a discussion of this.

and the reflector ndestructs or deflects the energy to 90 degrees of
impact.

That's more nonsense. You'd develop a much better understanding of
antennas (or any physical system) by developing and learning to apply
some basic math skills than by dreaming up alternate explanations for
well-known physical phenomena.

I don't believe I can help you any more -- if indeed I've helped you at
all --, and think (or at least hope) that most other readers have
understood what I'm saying. So I'll bow out here.

Roy Lewallen, W7EL